Control system



H. BANY CONTROL SYSTEM May 3, 1938.

Filed July 30, 1936 lnvehtor: Herman Ban kttorney.

Patented May 3, 1938 UNITED STATES CONTROL SYSTEM Herman Bany, Lansdowne, Pa, assignor to General Electric Company, a corporation of New York Application July 30, 1936, Serial No. 93,409

3 Claims.

My invention relates to control systems and particularly to systems for controlling the excitation of a synchronous motor of a synchronous motor generator set in accordance with the load on the generator thereof.

In certain types of electric systems of distribution, it is the practice to supply the current to a local load, such as an electric shovel, by means of a synchronous motor generator set. The

amount of current supplied to the load is varied by varying the excitation of the generator of the set. Heretofore, in such a system, there has been no regulation of the synchronous motor excitation as the load on the generator was increased.

Since a relatively high value of field excitation has to be applied tothe synchronous motor in order to prevent it from pulling out of step under certain operating conditions, it has been found that in some cases this high field excitation causes the power factor of the motor to be of such a leading value at no load as to be objectionable.

One object of my invention is to provide an improved arrangement for controlling the excitation 01' a synchronous motor so that under all load conditions the power factor thereof is oi such a value as not to be objectionable.

My invention will be better understood from the following description when taken in connection with the accompanying drawing, the single figure of which diagrammatically illustrates a synchronous motor field control arrangement embodying my invention, and its scope will be pointed out in the appended claims.

Referring to the drawing, 1 represents a synchronous motor generator set comprising a synchronous motor 2 connected to an alternating current supply circuit 3 and driving a generator 4, which is arranged to supply current to a load circuit 5. The motor 2 is provided with a field 4o winding 6, which is connected to a suitable source of excitation I through a suitable impedance, such as a resistor l. The generator 4 is provided with a field winding 9, which is arranged to be connected across a suitable source of excitation Ill through an adjustable rheostat l l The rheostat II has a movable contact member l2, which, when moved, varies the amount of resistance connected in series with the field winding 9. The rheostat II is also provided with a stationary contact I3,

which is arranged to be engaged by the movable member I! when it is in a position to produce an excitation of the generator field winding 9 in excess of a predetermined amount. When the contacts I! and ll are in engagement, a circuit is completed for a control relay ll, which, when energized, completes an energizing circuit for a field relay l5 to complete a shunt circuit around a portion of the resistor 8 and thereby increase the excitation of the motor field winding 6 a predetermined amount. Therefore, until the load on the generator exceeds a predetermined amount the motor excitation is maintained at a relatively low value to prevent the power factor of the motor from becoming too leading. However, when the generator load exceeds this predetermined 10 value, the motor excitation is increased to the desired value to produce the maximum pull-out torque.

In order to delay the de-energization of the relay ii for a predetermined time after the load 15 on the generator I has been decreased below a predetermined value, the relay l5, when energized, is arranged to complete a locking circuit for itself through the contacts of a time relay I6. The circuit of the operating winding of the time relay I6 is arranged to be completed by the relay 20 I when it is in its deenergized position. Therefore, when the movable contact member II of the rheostat Ii is moved out of engagement with the contact I3 and thereby effects the deenergization 01' the relay ll, the relay i5 does not operate to remove the shunt circuit from around a portion of the resistor 8 until sufllcient time has elapsed for the time relay ii to operate and open its contacts 20.

The operation 01' the arrangement shown in the drawing is as follows: Alter themotor 2 has been started and synchronized in any well-known manner, examples of which are well-known in the art, the movable member l2 oi the rheostat II is adjusted to vary the current supplied to the load circuit 5 by the generator 4. The contact I 3, which is adjustable is mounted in any suitable manner so that it is engaged by the movable contact II when it is in a position to efiect o an'excitation of the generator field winding 9 in excess oi a. predetermined amount. Therefore; when the movable arm I2 is moved to increase the generator field excitation above this predetermined value, the relay I4 is energized to close 45 its contacts I! and open its contacts it. By closing its contacts II, the relay l4 completes an energizing circuit for the relay l5, which in turn, by closing its contacts I9, completes a shunt circuit around a portion of the resistor 8 to efiect 50 a predetermined increase in the excitation of the field winding i. By opening its contacts la, the relay ll opens the circuit of the normally energized time relay I6. As soon as the relay l6 closes its contacts a, a locking circuit is completed for 55 j the field relay I! through its contacts 2| and the contacts 20 of the relay l6. Therefore, when the movable member l2 of the rheostat II' is moved out of engagement with the contact l3 and effects the deenergizatlon of the relay II, the relay I5 is not deenergized to remove the shunt circuit from around the resistor 8 until the relay H has remained deenergized for a suflicient length of time to allow the time relay I6 to open its contacts 20 in the locking circuit of the relay l5.

While I have, in accordance with the patent statutes, shown and described my invention as applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is;

1. In combination, a synchronous motor generator set, movable means for varying the excitation of the generator of said set, and relay means responsive to the position of said movable means for immediately increasing the excitation of said motor when said movable means is moved erator set, movable means for varying the excitation of the generator of said set, and relay means responsive to the position of said movable means for immediately increasing the excitation of said motor to a predetermined value when said movable means is moved to a position in which the generator excitation is increased above a predetermined value and for decreasing after a predetermined time delay the excitation of said motor to a predetermined value when said movable means is moved to a position in which the generator excitation is decreased below a predetermined value.

3. In combination, a synchronous motor having a field winding, a generator driven by said motor and having a field winding, means for supplying current to said field windings, an ad-- justable rheostat in series with said generator field winding, said rheostat having a movable member, and relay means responsive to the position of said movable member for effecting substantially immediately a predetermined increase in the excitation of said motor field winding when said movable member is moved to a position to increase the excitation of said generator field winding above a predetermined value and for decreasing the excitation of said motor field winding a predetermined amount when said movable member remains for a predetermined time in a position in which the excitation of said generator field winding is maintained below a predetermined value.

HERMAN BANY. 

